This invention relates to spinnerets and, more particularly, to a spinneret for the production of hollow filaments from synthetic polymers.
There have been various types of spinnerets proposed for the spinning of hollow filaments, and generally these include an insert fitted in the spinneret passage to provide an annular space at its outlet for the formation of the sheath of the hollow filament. The interior of the filament is prevented from collapsing by introducing a gas or drawing air into the center of the filament by means of passageways in the insert.
While prior art efforts to obtain a satisfactory spinning nozzle for the spinning of hollow filaments have been somewhat successful, the insert-type spinnerets of the prior art are susceptible to polymer leakage into the core fluid supply passageways because of a lack of a positive seal between the polymer and core supply fluid. For example, U.S. Pat. No. 3,397,427, of common assignee, discloses such a spinneret wherein a shaped insert is swaged into each passage of the spinneret to effect a seal between the insert and spinneret plate. In practice this design is subject to leakage of polymer into the air vent passages 34, 28 of the insert because thermal cycling during spinning operations, disassembly, cleaning and repair, and rebuilding causes expansion and contraction of the insert, breaking the swaged seal and allowing bottom surface 21 of the insert to come loose from shoulder 14 formed in the passage of the plate 11. Polymer then can leak into the air vent passages.